Vacuum tube system



Nov. 14, 1933. c. L. LAFFERTY 1,935,156

VACUUM TUBE SYSTEM Filed Sept. 1, 1928 IN VEN TOR W By% %.M.;

A TTORNEY Patented Nov. 14, 1933 UNITED STATES 1,935,156 VACUUM TUBE SYSTEM Charles L. Lafierty, Collingswood, N. J assignor by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application September 1, 1928. Serial No. 303,480 7 Claims. (01. 250-27) My invention relates to apparatus for supplying energy and regulating or controlling the energy supplied to an operating circuit of a vacuumtube,

In accordance with my invention, an electrical current is passed through the plate circuit of a vacuum tube and an effect is produced in a device connected to a circuit related to or paralleling said plate circuit, said device being connected to said second named circuit in a region where the voltage does not increase in response to increase of the current in said plate circuit.

Further inaccordance with my invention, an electrical current is passed through the plate circuit of one vacuum tube and the filament of an associated vacuum tube is brought to incandescence by current traversing conductors connected to points of different potential on a resistance structure in a region thereof where the voltage does not increase in response to increase of the current in said plate circuit. I

Further in accordance with my invention, current is obtained for the filament circuits on one or more amplifying vacuum tubes of a series thereof preceding the last stage amplifying tube from a source of current, the voltage of which does not increase in response to overloading of said last stage amplifying tube. V

For one of the forms my system or apparatus may take, reference is to be had to the accompanying drawing in which:

Figure 1 is a diagrammatic view of a vacuum tube system arranged in accordance with my invention. a

Figure 2 is a diagrammatic View illustrating a typical arrangement for supplying energy to the input circuit of an amplifying tube.

Referring to Figure 1, there is illustrated a transformer T having a primary winding 10 energized by alternating current of any suitable voltage and frequency such, for example, as that ordinarily applied to house lighting systems. Induce tively related to the magnetizable core of transformer T, in the example shown, are a plurality of secondary windings s1, s2 and s3.

The output circuit of winding s2 supplies current to a suitable rectifying system which comprises, in the example shown, the evacuated rectifying tubes 1 and 2 each having a cathode or filament 0 and an anode or plate a. Conductors of winding 81 are traversed by current sup-plied to theaforesaid cathodes c, 0 whereby they are brought to incandescence.

, Connected to the respective anodes a, a are conductors leading, respectively, to the terminals able magnetic system, not shown, to produce an 3 and 4 connected, respectively, to the terminals 1 of winding s2 while the mid-point of said winding s2 hasa conductor 5 connected thereto which, with a conductor 6 connected to the aforesaid conductor 4, forms a circuit traversed by rectified current, the filter system comprising the condensers K, K1 and the inductance I causing the delivery of direct current of substantially constant magnitude to the positive and negative terminals of a resistance structure R, connected across said conductors 5 and 6. From the resistance structure R, current is supplied to the operating circuits of thermionic or vacuum tube apparatus by conductors suitably connected to points of different potential on said structure R.

Still referring to Figure 1, there is illustrated a pickup device P, the terminals .of which are connected in a circuit comprising the conductors 7 and 8 connected to the primary winding of a suitable audio frequency transformer T1, the circuit comprising said conductors 7 and8 prefera- .bly includes a potentiometer 10 for'controlling electrical quantity varying in accordance with the vibrations of the stylus 11 as imposed by the aforesaid phonograph record.

Associated with the secondary winding of transformer T1 is an amplifying vacuum tube or thermionic device 12 which comprises the usual filament fl, grid g1 and plate 121. The grid g1 is connected to one terminal of the secondarywinding of transformer T1, the other terminal of which is connected to the resistance structureR by a conductor 13. The filament fl is brought to incandescence by current supplied to its terminals by conductors l4 andrl5 connected, respectively, thereto and to separated points on the resistance structure R. The plate 111 has connected thereto a conductor 16 which extends to the resistance structure R, said conductor 16 including the primary winding of an audio frequency transformer T2.

A second amplifying vacuum tube or thermionic 1 device 17 also comprises the usual filament f2, grid g2 and plate 112. The grid 92 is connected by a conductor 18 to the negative terminal of resistance R, said conductor 18 including the'sec- The terminals of filament 12 are connected, respectively, by conductors 19 and 20 to the respective terminal of secondary winding 33 of transformer T, a conductor 21 branching from the mid-point of said winding .93 and being connected to the aforesaid conductor 13. The plate $2 is connected to the positive terminal of resistance R, by a conductor 22 which includes the primary winding of an audio frequency transformer T3.

Connected in a circuit including the secondary winding of transformer T3 is an energy-translating device E which, for example, may be a loud speaking telephone of any suitable type well known to the art.

As described above, alternating current is supplied to the primary winding of transformer T and is rectified by the tubes 1 and 2 which, in conjunction with the above described filter system, produces direct current of substantially constantand unvarying magnitude for application across the terminals of the resistance structure R.

- J The filament or cathode of the amplifying vacuum tube 17, in the example shown, is brought to incandescence by alternating current supplied from the secondary winding's3 of transformer T. The filament or cathode of the amplifying vacuum tube 12, however, is brought to incandescence by direct current, since the conductors 14 and 15 branching from the respective terminals of filament f1 are so connected to the resistance R that the drop inpotential across said conductors causes a current of desired magnitude to transverse the aforesaid filament fl.

The current in the output or plate circuit of the vacuum tube 12 is derived'from resistance R and traverses a path including the conductor 16 and one of the conductors connected with the filament Similarly, the current traversing the output or plate circuit of vacuum tube 17 is derived from the resistance R and traverses a path including conductors 22 and 21, the latter, as described 1 above, being conductively related to the filament of said vacuum tube 17. In the example shown, the vacuum tube 17 is of higher rating or greater capacity than the vacuum tube 12 inasmuch as the current traversing the plate circuit of said vacuum tube 17 is of substantially greater magnitude than that which traverses the plate circuit of vacuum tube 12; hence vacuum tube 1'? is of the type known to the art as a power amplifier.

As is obvious from the drawing, the output circuit of vacuum tube 12 is inductively related to the input circuit of vacuum tube 17 by the transformer T2, the latter serving to transfer energy from said output circuit to said input circuit. Similarly, the output circuit of vacuum tube 1'? is inductively related to the circuit of the energy-translating device E by transformer T3 and, accordingly, energy is transferred from said last named output circuit to the local circuit of the device E. Under some circumstances in the ordinary operation of the aforesaid vacuum tube system, the Vacuum tube 1'? may be overloaded, for example, by the application to its grid 2 of voltage having an excessive or unusually high magnitude. With some arrangements of the prior art, current for bringing to incandescence a filament, such as the filament fl of tube 12, is obtained from a resistance structure, such as the herein disclosed struc-. 'ture R, in a region thereof wherein the voltage increases in magniture when said last stage am plifying tube is overloaded. With such an arrangement, there exists a vicious circle, overloading of the last stage vacuum tube causing a preceding tube to take more energy, this added energy, in turn producing further overloading of the last stage tube. Such operation of a vac uum tube system is unstable and produces unsatisfactory reception in the device E.

In accordance with invention, the aforesaid unsatisfactory operation of the vacuum tube system is overcome by providing an arrangement wherein the heating current for the vacuum tube or tubes preceding the last stage tube is obtained from the resistance R in a region thereof where the voltage does not increase when the tube 17 is overloaded. More specifically, in accordance with my invention, the aforesaid filament heating current is obtained from the resistance R in a region thereof wherein the voltage decreases in response to overloading of the tube 17. Thus, in the example shown, the resistance R is disposed in parallel relation with respect to plate circuit of vacuum tube 17 and, when the input circuit of the latter is overloaded, the current in its plate circuit increases in magnitude and a corresponding drop in voltage occurs across the resistance R in the region thereof between which the conductors 21 and 22 are connected.

It is a prominent feature of my invention that the filament heating current for one or more tubes preceding the last stage amplifying tube is obtained from this last mentioned region of the resistance R and, accordingly, when the last stage tube 1"! is overloaded, the input energy of the pre ceding tube or tubes is decreased in magnitude.

It shall be understood that my invention is not to be limited to an arrangement wherein filament heating current is obtained as described above for, under some circumstances, it may bedesir able to obtain grid biasing voltages from the aforesaid region of resistance R for one or more tube or tubes preceding the last stage amplifier tube.

It shall be understood that various arrangements other than that illustrated in Figure 1 may be utilized for supplying energy to the amplifying vacuum tube 12. Thus, as shown in Figure 2, there is shown an alternative supply arrangement wherein the input energy is derived from a radio receiving system. To this end, the primary winding of transformer T1, in lieu of its connection to a pickup circuit, is connected to the detector tube 25 of a radio receiving system. The tube 25 comprises the usual filament f3, grid g3and plate p3, the output or plate circuit of said tube 25 including a source of current 26 and being connected to the primary winding of transformer T1. As illustrated in Figure 2, the filament is brought to incandescense by a battery 27, or the like. The input circuit of tube 25 comprises the usual grid leak 28 and associated condenser 29, and said input circuit may be tuned by a variable condenser '30. Connectedjto the terminals of said input circuit is the secondary winding of a radio frequency transformer T4,-the

primary winding of which may be associatedwith 14@ 1. In combination, a plurality of vacuum tubes in cascade, and a potentiometersupplying energy 50 to said tubes, the filament of one of said tubes being connected to a portion of said potentiometer wherein the current does not increase when the plate current of a succeeding tube increases, a source of alternating current for energizing the cathode of said succeeding tube, and a connection, independent of the means for supplying plate current to the first-mentioned vacuum tube, extending between the cathode current supply means and the grid of theother tube.

2. The combination of a vacuum tube comprising cathode, grid and plate electrodes, means for supplying current to the plate circuitof said vacuum tube, separate means for supplying current to said cathode, a second vacuum tube connected in cascade with said first mentioned tube and in the input thereof, at least one of the input electrodes of said second named tube being connected to said plate current supplying means in a region where the voltage does not increase in response to increase of the current of said plate circuit, and a connection for supplying plate current to the first-mentioned vacuum tube, extending between the cathode current supply means and the grid of the other tube.

3. The combination with a vacuum tube'comprising cathode, grid and plate electrodes, means for supplying current to the plate circuit of said vacuum tube, separate means for energizing said cathode, of a second vacuum tube connected in cascade with said aforementioned tube and in the input thereof, the cathode of said second vacuum tube being connected to said plate current supplying means in a region thereof where the voltage does not increase in response to increase of the current in said plate circuit, and a connection for supplying plate current to the first-mentioned vacuum tube, extending between the cathode current supply means and the grid of the other tube.

4. The combination of a vacuum tube comprising cathode, grid and plate electrodes, means for energizing said cathode with alternating current, a second vacuum tube connected in cascade with said afore-named tube, means comprising a potentiometer structure for energizing an electrode in the input circuit of said second named vacuum tube and the plate and grid electrodes of said first named tube, said input electrode of said second named tube being connected to said potentiometer structure in a region where the voltage does not increase in response to an increase of the plate current in the first named tube, and a connection for supplying plate current to the first-mentioned vacuum tube, ex-

tending between the cathode current supply means and the grid of the other tube.

5. The combination of avacuum tube comprising cathode, grid and plate electrodes, means for supplying space current to the plate circuit of said vacuum tube, separate means for supplying cathode current to said tube, a second vacuum tube connected in cascade with said afore-named tube and in the input thereof, means comprising a potentiometer structure connected in shunt with said plate circuit, the input electrodes of said second named tube being energized from said potentiometer, and a connection for supplying plate current to the first-mentioned vacuum tube, extending between the cathode current supply means and the grid of the other tube.

6. The combination, of a vacuum tube comprising cathode,grid and plate electrodes, means for supplying space current to the plate circuit of said vacuum tube, separate means for supplying current to said cathode, a second vacuum tube coupled to said first named tube, means comprising a potentiometer structure connected in shunt with the plate circuit of said first nalned tube for energizing the filament of said second named tube, whereby the voltage across the terminals of said filament does not increase in response to increase of the current in theplate circuit of said first named tube, and a connection for supplying plate current to the firstmentioned vacuum tube, extending between the cathode current supply means and the grid of the other tube.

7. The combination of a vacuum tube comprising cathode, grid and plate electrodes, means for supplying space current to the plate circuit of said tube, separate means for supplying alternating current to said cathode, a second vacuum tube coupled with said afore-named tube in signal transferring relation, means comprising a resistance structure connected in shunt with the plate circuit of said first named tube for energizing the filament of said second named tube with direct current, said last named filament being connected to said last named means in a region where the voltage decreases in response to increase of the current in the plate circuit of said first named tube, and a connection for supplying plate current to the first-mentioned vacuum tube, extending between the cathode current supply means and the grid of the other tube. r 7

CHARLES L. LAFFERTY. 

